VIDEO: Helicopter Goes Down in Fiery Crash

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(Photo Courtesy: youtube /Nic Walker)

VIDEO: Helicopter Goes Down in Fiery Crash

(Photo Courtesy: youtube /Nic Walker)

By Laura Smith-Spark

LONDON (CNN) — A helicopter crashed into a construction crane atop a new building in thick London fog Wednesday, killing two people and sparking a line of flame when it plunged to the ground.

Nine others were injured in the crash that took place at the height of the morning rush hour in Vauxhall, south of the River Thames in central London.

One was critical, but police said the others did not appear to be seriously hurt.

The crash did not appear to be terrorism-related, police said.

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James Whipps, a CNN producer, said the helicopter wreckage appeared to have landed on two cars near the site of St. George Wharf, a major residential construction project.

Another eyewitness said firefighters pull three injured people from two burning cars.

Thick smoke and flames billowed into the sky. The bent crane dangled from the building top, prompting police to cordon off roads in the area.

The St. George Wharf construction project includes the landmark St. George Wharf Tower, also known as the Vauxhall Tower. Its builders say it will be one of Europe’s tallest residential towers.

“I was standing outside having a cigarette when I saw the helicopter flying super fast towards the crane,” said Rezart Islami, a builder who was working across the street from the 52-story building. “The pilot appeared not to have seen the crane because the helicopter hit it and went bang.”

Islami said the rotor blade snapped off, the copter spun to the ground and burst into flames.

“The top off the crane also came off in the impact,” he said. “It all happened so fast it was unbelievable.”

Whipps said he heard the sound of the helicopter rotors suddenly cut out.

He did not see the impact but as he looked though a window, he “suddenly saw this enormous fireball, black smoke, shoot up from the side of a building.”

No cause but poor visibility

Many helicopters follow the Thames as a flight route through the city. This helicopter appeared to be flying further south than usual, Whipps said.

Vauxhall, not far from Westminster, is where a new U.S. Embassy is being built.

The area, which is a mix of industrial, business and residential use, is also home to the headquarters of the UK intelligence service, MI6.

No cause has yet been given for the crash but visibility was poor in London on Wednesday morning, with fog and a very low cloud ceiling.

Chris Yates, an aviation security expert, told CNN it was likely there would be questions about whether the helicopter should have been flying in these conditions.

Under safety regulations, tall buildings must have navigation lights on top to make them apparent to low flying aircraft, he said.

Helicopters are not supposed to fly within 500 feet of tall structures in central London, he said.

The incident is likely to cause major disruption for many people on their way to work.

Vauxhall, with a rail station, Underground station and large bus station is an important transit point for those traveling from the south to other parts of London.

South West Trains said passengers should take alternative routes.

“Police have cordoned off a significant area this includes Vauxhall Rail, Bus and Underground stations. Trains are still running into and out of Waterloo but will not stop at Vauxhall station to set down or pick up passengers,” its website said.